Blastomycosis, hereafter called blasto, is an infection caused by the fungus Blastomyces dermatitidis (B. dermatitidis). Although it occurs primarily in humans and dogs, it has also been observed in cats and horses. Blasto can affect most organs, including the brain and eyes. This disease can be every bit as devastating as the most vicious kind of cancer, and not all blasto victims survive despite aggressive treatment.

Blasto can easily be misdiagnosed since it shares some of its symptoms with other diseases. In fact, a dog may die before the correct diagnosis is established. The fungus grows as a mold in moist acidic soil rich in decomposing organic matter, including sandy soil, especially around bodies of water such as Lake Michigan. The fungus was recently isolated in rotting wood in Northern Wisconsin, yet in a second attempt to isolate it in the same location it was no longer found. Blasto is considered endemic in the southcentral, southeastern and midwestern United States, as well as some areas in Central and South America and parts of Africa. It was previously thought to occur only east of the Mississippi. However, several years ago blasto that occurred in several people was traced to a construction site near Boulder, Colorado. This is far outside the areas considered as endemic. The fungus has been reported to occur in soil from barns, a chicken house, a cattle crossing, and an abandoned shack. Cattle and chickens could have carried the fungus on their feet, and the wood in the abandoned shack may have been decomposing.

The elusive fungus seems to exist in “pockets.” If we translate this to dog kennels, it may be in one kennel but not in the neighbor’s. Blasto does not seem to have a favorite season, since it occurs year-round. Thus, it is safe to say that it is resistant to freezing. It has been diagnosed in the Thunder Bay, Ontario area, but no reports are available about occurrence of the disease in Alaska. This, however, does not mean that it does not exist there or in other nordic regions.
The fungus releases spores that can be inhaled by both animals and people. After the spores enter the lungs or other tissues they begin to multiply, leading to infection. If this process continues in the lung, severe pneumonia results. The disease may remain in the lung, or, as mentioned above, it may attack other parts of the body, including the eyes, skin, brain, joints, lymph nodes, urogenital and digestive systems and even invade the bones. Daniel P. Paretsky, DVM, owner of the Eagle River, Wisconsin Animal Hospital, found the organism in heart muscle during necropsy in one dog. If the spores enter an open wound, a local infection can occur. However, the most common form of blasto is the generalized form following inhalation, from which no organ is safe.

According to Dr. Paretsky, who treats about 15 to 20 dogs (some of them sled dogs) with blasto per year, “A definite length of incubation has not been established. Our best guess is about six weeks, although the fungus may lay dormant longer in some animals or take less time to manifest itself in others.”

Outdoor dogs (especially hunting dogs, but also sled dogs) are at highest risk for blasto. During one season, namely winter, Dr. Paretsky saw three sled dogs with blasto in one kennel.

City dogs are not safe from blasto, either. A 3-year-old Doberman belonging to a friend of mine succumbed to blasto two years ago. For several months the dog’s obedience instructor noticed that her gait was “off,” but this was almost imperceptible. Subsequently the dog developed a fever and a cough, severe fatigue and loss of appetite, plus severe lameness. These symptoms came on suddenly, and the dog died before all the diagnostic work was completed. This dog was a pampered apartment dog, and her only outdoor activities were being walked on the sidewalk and visiting the dog park.

Among humans, the most endangered are farmers, construction workers, forestry workers, campers, hunters, and gardeners, anyone having contact with soil, especially when digging deep.

The average age of dogs contracting blasto is 3 years. Some but not all studies have reported a higher incidence in males. Dr. Paretsky has observed a slightly higher incidence in males as well, “But I attribute that to more roaming and digging behavior than to susceptibility,” he says.

Symptoms of blasto usually vary, depending on the organ or organs affected. They may include one, several or all of the following: loss of appetite, depression, weight loss, a temperature of 103 degrees or higher (which may spike and drop), exercise intolerance, coughing, and limping. Skin lesions can appear anywhere on the body, even inside the mouth. The lesions can hemorrhage suddenly. Lymph nodes are usually enlarged, and one eye or both eyes may be inflamed or appear cloudy.

The diagnosis of blasto usually includes examining samples from draining skin lesions or a lymph node under the microscope, chest X-rays, a complete blood count (CBC) and chem screen. The latter is done in order to rule out other causes of the symptoms, but will not diagnose the presence of the fungus. Fungal titers in the blood confirm the diagnosis. One problem with the titers is that sometimes the tests are negative despite unmistakable signs of blasto. “If, based on a physical examination, I suspect blasto,” says Dr. Paretsky, “I take X-rays of the chest, or of a limb if I think the fungus might be in the bone. Chest X-rays in a dog with blasto have a blizzard-like appearance. I like a definitive diagnosis based on identifying the organism from material drawn from an abscess or a bony lesion, or in sputum generally collected under anesthesia. If I can not identify the disease in this manner, I may submit blood to the lab to check for antibodies.”

In my personal experience with three cases of blasto in my own kennel (one in 1978 and two in 2003) monitoring the fever spikes helped confirm the presence of the disease in the last two dogs. If you observe a cough in a dog or notice sudden lameness without apparent cause, (such as an accident or other known problem) skin lesions or eye inflammation, contact your veterinarian immediately. While waiting for your appointment you may want to start taking the dog’s temperature about every two hours. Record the times and numbers observed. This can be helpful in establishing a diagnosis. A digital ear thermometer can make it easy to take the temperature often, but I find digitals less accurate than the old mercury-filled rectal thermometers. Therefore, if you still have one of those, you may compare the first one or two measurements to learn what the possible difference is.

Survival depends on early diagnosis and treatment. It is estimated that about 85 percent of treated dogs survive. However, even after successful treatment the fungus can remain dormant for years and then recur, but the probability of recurrence diminishes as time goes on. The relapse rate reported in the literature is about 25 percent, compared to only about 5 percent in Dr. Paretsky’s patients. Perhaps the lower relapse rate observed by Dr. Paretsky is attributable to very careful monitoring of the dogs during and following completion of therapy. “We see dogs where the disease flares up as soon as we back off the medication,” says Dr. Paretsky. “Some of our patients have been on medication for two or three years.”

My first dog with blasto, a one-year-old malamute, was diagnosed too late. Only the third veterinarian I consulted believed that it could be blasto. By that time the dog’s condition had deteriorated so far that survival was doubtful, and I decided to euthanize the dog. The second dog, a 7-year-old Siberian sled dog lost one eye to the disease and later lost the second eye. In this dog (he is now 12 years old and has adjusted well to his blindness) only the eyes were affected. The third dog, a 6-year-old Siberian lead dog, was affected in the most severe way. First came the cough, then he began to limp on one leg, and finally a second leg was affected. Meanwhile the fungus was not found in the blood and he was treated with antibiotics for pneumonia, followed by a worsening of his condition. After blood suddenly started gushing from under his tongue where I discovered a huge gaping hole, without exaggeration more than ½cm in diameter, blasto was diagnosed. Samples from the lesion showed the fungus under the microscope.

Usually dogs with involvement of the eyes have a poorer prognosis, because medication is not well absorbed by the eyes. Dr. Paretsky believes in removing the infected eye at some point during treatment because it may serve as a source for chronic infection. Not all veterinary ophthalmologists agree on this point; however, says Dr. Paretsky, “I prefer to err on the side of caution.”

Likewise, dogs with poor liver or kidney function do not do very well because these organs cannot handle the strong antifungal medication efficiently or may not even tolerate treatment. Survival is also less hopeful in older dogs due to diminished organ function. For this reason, as well as the expense of the medications, some owners choose euthanasia.

My Siberian with the multiple-organ involvement survived the first bout of blasto and was doing well after four months of treatment. He relapsed nine months later, two weeks after I euthanized his companion and playmate, a 14-year-old female, after she suffered a stroke. The male cried intermittently for a week after her death. I attribute this dog’s relapse to stress following the loss of his companion. This time the disease struck more viciously than the first time, involving many organs. Most severely affected were the stomach and intestines, and he was hemorrhaging blood from both. I decided to end the dog’s suffering.

After this ordeal I have never relaxed when it comes to blasto. Since all three of my dogs that contracted blasto were enthusiastic diggers, I have tried to minimize digging as much as possible, even though their excessive digging may have been purely coincidence. As a small contribution to my peace of mind, I had the entire team hookup area, where most of the digging took place, covered with cement blocks.

Several medications are available to treat blasto, none of them without possibly severe side effects. For years amphotericin B was the standard treatment for blasto. Although several other antifungal drugs are now available, some veterinarians still consider amphotericin a good choice for severe cases, with improvement usually occurring in three to five days. Drawbacks to this drug are administration by the intravenous route one to three times per week and the possibility of severe kidney damage. Ketoconazole administered orally has a lower cure rate than amphotericin, but can be useful in a dog with poor kidney function and a mild form of the disease. Improvement may take 10 to 14 days. These two medications can work well when given together, which makes it possible to lower the dosage of amphotericin, thus minimizing the risk of kidney failure. The main side effect of ketoconazole is liver toxicity.

Itraconazole and fluconazole have been shown to be highly effective against blasto. They are given orally, and although improvement is usually observed rapidly, they must be administered for 2 to 4 months or longer because of the high probability of a relapse. Their main adverse effects are liver toxicity. The latter two drugs are Dr. Paretsky’s drugs of choice. “I use them somewhat interchangeably. If one doesn’t seem to work fast enough, I switch to the other one, and on occasion I use them in combination,” says this very experienced clinician. In his opinion fluconazole appears to be the drug of choice for central nervous system involvement.
The response to treatment with itraconazole and fluconazole is usually within days, but a dog’s condition may worsen temporarily due to the massive die-off of the fungus before improvement returns. Although the latter two drugs are considered the most effective treatment choices, their cost can be a drawback. My cost for the treatment of the two Siberians amounted to over $3,500. Unfortunately, I had to use Sporanox® (the proprietary form of itraconazole) the first two months of treatment because the generic form was not available to me. If the generic form of these drugs is used, the cost of treatment is considerably less.

Another question remains. Is blasto contagious? Although none of the experts say it can not happen, this infection is not generally considered contagious. However, you and your other dogs may be at risk through a common environmental source, which may be on your property or places you and your dogs have visited. Caution is advised when you handle your dog’s lesions, and it is best to wear surgical gloves. This applies especially to people with a depressed immune system, for example due to treatment of another condition with corticosteroids.
Being aware that the disease may be endemic in your area, and having a dog checked right away if you observe signs of respiratory problems, skin or eye infections or lameness, is all that you can do. Since these symptoms can belong to several different conditions (such as Lyme disease if a dog is limping and has a fever,) start checking for fever spikes while waiting for your appointment, so you can help your veterinarian establish a sometimes difficult diagnosis.

Karen Gadke, PhD (Health Science) is a clinical study specialist, medical writer, author and lecturer. She has been mushing and racing since 1979. She owns both Siberian and Alaskan huskies.

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